Tibial plateau leveling osteotomy (TPLO) procedures are well known in the veterinary art. Tibial plateau leveling osteotomy procedures are used to correct ruptured cranial cruciate ligaments for various animals, primarily for canines. These procedures provide an alternative therapy to ligament repair procedures. Today, tibial plateau leveling osteotomy procedures have become the standard of care for medium and large canines.
By way of background, the cranial cruciate ligament stabilizes the canine's stifle joint (called the knee for humans). One of the important functions for the ligament is to control the sliding of the upper femur bone on the lower tibia bone. Unfortunately, however, for many canines the ligament partially or fully ruptures. The tibial plateau leveling osteotomy procedure provides a way to correct this problem.
The tibial plateau leveling osteotomy procedure is well documented in the art. For example, the procedure is described in U.S. Pat. Nos. 4,677,973 and 5,304,180, both of which are incorporated herein in their entirety. The procedure is also described at the web site www.vetsurgerycentral.com/tplo. Basically, a curvilinear cut is made to the upper portion of the tibia. This cut portion of the tibia is then rotated on the order of about 20-30 degrees thereby creating a more level plane or surface on the top of the tibia upon which the femur can rest. The cut and repositioned portion of the tibia is then secured to the lower portion of the tibia.
Various means have been used to fix and secure the cut portion of the tibia to the remaining portion of the tibia. Initially, screws and wire were used for this purpose. Later, those in the art used metal plates that were anchored into the tibia in both the bottom portion and upper, cut portion by way of bone screws. The problem with many plates currently in use is that they require the surgeon to manipulate the plate to conform to the tibia during the surgical procedure. This is often difficult because the plates are relatively thick and rigid, and thus are not easily bent into an acceptable shape. Furthermore, bending of the plate during the procedure can result in the screw holes becoming deformed.
Another drawback with the TPLO plates currently available is that the screw holes in the plate for use with the upper, cut portion of the tibia are not designed for optimum fixation. Improved designs for screw placement into the tibia are needed to avoid the screws from being located near a cut portion of the tibia or near the articular surface of the tibia and the femur.